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dhcp: don't add route to DHCP4 server

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This basically reverts commit 31fe84e467 "core: Add host route for
DHCP4 server if outside assigned subnet (bgo #721767)" because the
additional route added by NM does more harm than good.

First, the code does not consider routes pushed by the server and thus
it can add a route conflicting with the ones from the network
administrator.

Second, there is no specification on what a DHCP client should do when
the server is not reachable via unicast, and adding arbitrary logic
into the client is likely to break things in specific cases. If
network administrators want to make the DHCP server reachable from a
client in a different subnet, they should push proper routes with the
lease.

In any case, if the DHCP server is not reachable through unicast,
before the lease expiration (after timeout T2) the client will resort
to broadcast and so there won't be any network disruption; the renewal
will only happen at a later time.

Fixes: 31fe84e467

https://bugzilla.redhat.com/show_bug.cgi?id=1448987
(cherry picked from commit 36e97f5d7b)
This commit is contained in:
Beniamino Galvani 2017-05-10 16:17:48 +02:00
parent 8ca05e9fd2
commit cbf5a776f7
1 changed files with 0 additions and 37 deletions
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37
src/dhcp/nm-dhcp-utils.c
View file

@ -450,43 +450,6 @@ nm_dhcp_utils_ip4_config_from_options (int ifindex,
}
}
/*
* RFC 2132, section 9.7
* DHCP clients use the contents of the 'server identifier' field
* as the destination address for any DHCP messages unicast to
* the DHCP server.
*
* Some ISP's provide leases from central servers that are on
* different subnets that the address offered. If the host
* does not configure the interface as the default route, the
* dhcp server may not be reachable via unicast, and a host
* specific route is needed.
**/
str = g_hash_table_lookup (options, "dhcp_server_identifier");
if (str) {
if (inet_pton (AF_INET, str, &tmp_addr) > 0) {
_LOG2I (LOGD_DHCP4, iface, " server identifier %s", str);
if ( nm_utils_ip4_address_clear_host_address(tmp_addr, address.plen) != nm_utils_ip4_address_clear_host_address(address.address, address.plen)
&& !nm_ip4_config_get_direct_route_for_host (ip4_config, tmp_addr)) {
/* DHCP server not on assigned subnet and the no direct route was returned. Add route */
NMPlatformIP4Route route = { 0 };
route.network = tmp_addr;
route.plen = 32;
/* this will be a device route if gwaddr is 0 */
route.gateway = gwaddr;
route.rt_source = NM_IP_CONFIG_SOURCE_DHCP;
route.metric = priority;
nm_ip4_config_add_route (ip4_config, &route);
_LOG2D (LOGD_IP, iface, "adding route for server identifier: %s",
nm_platform_ip4_route_to_string (&route, NULL, 0));
}
}
else
_LOG2W (LOGD_DHCP4, iface, "ignoring invalid server identifier '%s'", str);
}
str = g_hash_table_lookup (options, "dhcp_lease_time");
if (str) {
address.lifetime = address.preferred = strtoul (str, NULL, 10);